The manipulator, as described herein, is controllable by state-of-the-art programmable controls. In combination with such programmable controls, the described manipulator becomes a robotic apparatus which duplicates by preprogrammed control commands handling operations which in the past have been performed by operators as manual operations. In efforts to avoid manual handling procedures in typically ultra-clean environments of integrated circuit manufacturing operations, it appears desirable to apply the operation of such a manipulator to handling semiconductor wafers in certain process steps, as, for example, a typical plating operation. Handling semiconductor wafers relative to a plating operation typically involves unloading the wafers, one by one, from a wafer magazine wherein the wafers are stored in a parallel, rather closely spaced arrangement, and transferring them to a plating rack. When held by the plating rack, the wafers are placed into a plating tank wherein they remain for a predetermined period. Thereafter, the wafers are rinsed and are then transferred from the plating rack to another magazine.
One of the problems encountered in attempts to use a manipulator for handling semiconductor wafers in connection with, for example, the described plating operation, relates to locating each of the wafers in the referred-to magazines by preprogrammed three-dimensional motion of the manipulator. The wafers are typically in a range of three to five inches in diameter, but are only about 0.020 inch thick. Detecting the presence or absence of contact between a wafer of such thickness and a handling tool presents a problem.
Another problem of using the manipulator in handling wafers with respect to the referred-to plating operation relates to inefficiencies which arise out of prolonged plating periods in each plating cycle during which the manipulator remains idle. If such idle periods can be used by the manipulator to perform added operations, the cost of the manipulator may be averaged over all of its performed operations for a lower average cost per operation. It is, therefore, desirable to extend the operation of the manipulator to perform similar handling operations with respect to a second plating facility. Such added operation, however, enlarges the space which the manipulator needs to traverse. Mechanical tolerances and vibrations in an extended range of motion have been found to become a problem unless the sizes of the moving mechanisms are appropriately increased for such extended range of motion. However, increased sizes of mechanical components also increase the weight and the cost of an apparatus. It is also more difficult to maintain dimensional precision in relatively larger apparatus components. The problem is one of an incompatible range of motion in at least one direction or dimension with respect to the range of motion in the apparatus in another dimension.